I. Field of the Invention
The present invention relates to power line carrier communications systems. More particularly, the present invention relates to a novel apparatus for transferring data in power line carrier communications systems.
II. Background Art
Power line communications systems have recently become a viable alternative as a communications link in many applications. Although various other data links such as optical, RF, ultrasonic and hardwire links have advantages in certain areas each one has limitations upon its applicability. For example, optical links operate only by line of sight, RF links are restricted by numerous regulations, ultrasonic links are interrupted by walls, and hardwired links require costly installation of signal carrying lines. With the power line carrier communication system as an alternative, pre-existing AC power lines may be utilized in the communications link.
In many applications such as building energy management schemes, power line communications systems enable the retrofitting of existing buildings to become a fairly simple task. By using the AC power line, no after-market installation is required for installation of remote control modules which control energy consuming devices such as compressors, motors, heating and air-conditioning and lighting. These remote control units and additional sensor units may communicate over the power line.
Utilization of the AC power line as a communications medium permits data to be transferred directly over the AC power line along with the normal AC current. The AC power line not only contains the typically 120 volt RMS of unwanted signal but also kilo-volt spikes which presents fundamental design challenges for carrier current transceiver circuits. In industrial environments, unwanted noise from motors, compressors and other industrial equipment generate even greater amounts of noise which may cause error in the data transmitted over the power lines.
In many applications the store input power is stepped down in voltage by a transformer to support lower voltage operating equipment. While certain other store equipment use the higher voltage input power, it is necessary to communicate between modules controlling equipment coupled to either power line. The step-down transformer does not permit low level signal communications of the power line carrier type to be transmitted between different voltage power lines. With data signals in the millivolt range and at a significantly higher frequency than the AC current, the transformer does not permit coupling of the signals from one side of the transformer to the other. In these situations, it is necessary to have a transformer bridge which permits coupling of the signal between the primary and secondary of the transformer while unaffecting the transformer voltage stepping-down characteristics.
The bridge module is utilized in addition to coupling data messages around the transformer, as a repeater to enhance data transfers between distant modules where normal signals face increased attenuation. With the bridge module operating as a repeater, the module may be used in systems where the input power supplies the same voltage power to all store equipment. The bridge module in application may also be used to provide communications between modules located on different phased lines of a multiple phased power line system.
It is therefore an object of the present invention to provide a novel and improved power line communication system transformer bridge capable of transferring data around a transformer.
It is yet another object of the present invention to provide a power line carrier communications repeater for enhanced reliability of network communications.